New Mobo, lower hashrate :-( Why?

Hi friends,I've been mining for a couple of months now, with a basic rig setup of single GPU R9 380x on a Gigabyte 970 AM3+ motherboard (all pre-used hardware).My setup and settings are posted here for details.After a recent thermal paste renewal on the GPU heatsink, and adding a couple of fans to the casing, I was getting a decent ~25.3 MH/s on this setup. But few days ago, the motherboard went kaput and the PC just went dead. Ofcourse I verified the Mobo as the culprit, by plugging in another PSU.Now I got another used Mobo, an MSI 970A-G43, keeping all the rest hardware the same. The PC is back online now, and after installing/updating all the required drivers, as I started mining again, the hashrate now showing just ~20.07 MH/s. I even checked the Bios settings of the new Mobo and set everything to "no power saving" and set for high performance, but don't see any improvements to the hashrates.Now 'm really at my wit's end; can't figure out why the hashrate dips so low all of a sudden?Can any one please point out what I can check/change to get my 24-25MH/s back again?